Electron diffraction study of the molecular structure ofo-chloroanisole using a dynamic nonparametrized model

Abstract

The geometrical parameters of the o-chloroanisole molecule were determined by gas phase electron diffraction in terms of the dynamic model using vibrational spectroscopy data and quantum chemical calculations. A new approach based on Tikhonov's regularization method is used to explicitly define the internal rotation potential of the methoxy group. It was found that the nonparametric internal rotation potential has two minima, one of which corresponds to the planar (ϕ=0°) and another to orthogonal (ϕ=90°) orientation of the O−CH3 bond relative to the plane of the benzene ring. The difference between the energies of the orthogonal and planar conformers is 0.9–1.0 kcal/mole, and the height of rotation barriers at ϕ≊65° is 1.4–1.6 kcal/mole, which confirms the results of quantum chemical calculations, indicating that the orthogonal conformer is present in substantial amounts (∼30%). The following basic geometrical parameters were found (ra in A, ∠α in deg, the error equals 3σ): r(C−C)ave=1.398(4); r(O−CPh)=1.358(36); r(O−CMe)=1.426(21);r(C−Cl)=1.733(4);r(C−H)Ph=1.086(6);r(C−H)Me=1.095(6); ∠CCOCCl=118.7(2.2); ∠COCC=119.9(2.5); ∠COCClC=121.5(1.1); ∠COC=117.6(2.6); ∠COCCl=119.1(2.1); ∠CCO=124.7(1.2). The results are compared with the data for related compounds. Stereochemical features of o-anisoles that are responsible for the orthogonal conformer are discussed.